The use of biometric identification systems is becoming ever more widespread for uniquely identifying people. The majority of known biometric identification systems use one or more intrinsic physical characteristics of a person for identification purposes. The accuracy of a biometric identification system is dependent on the uniqueness of the selected physical characteristic.
The iris is an example of a unique physical characteristic suitable for use in biometric identification systems. Such biometric identification systems generically referred to as iris recognition technology, have become increasingly popular. One advantage of this technology over other known biometric technologies is that iris recognition technology has the smallest outlier (those user's who cannot use the system) group of all known biometric technologies. For this reason it is considered to be the most suitable biometric identification technology for mass use. Furthermore, due to the speed of comparison of iris recognition identification systems, it is the only known biometric technology well-suited for one-to-many identification.
Known iris recognition identification systems use pattern-recognition techniques to uniquely identify an iris pattern from a captured image of the irides of an individual's eyes. U.S. Pat. No. 5,291,560 discloses an example of a known iris recognition identification system, and describes in detail how such systems work. The article “How Iris Recognition Works”, published in IEEE Transactions on Circuits and Systems for Video Technology, Vol. 14, No. 1, January 2004, authored by John Daugman, who is incidentally the inventor of the afore cited patent, provides a discussion of the underlying principles explaining how iris recognition identification systems work.
In order for iris recognition identification systems to provide accurate identification verification results, a clear and sufficiently high resolution image of the iris and/or irides must be captured, wherefrom the required iris pattern detail may be determined. Unclear images or low resolution images of the iris and/or irides can increase the rate of false negative verification results.
The formation of undesired “optical artifacts” in the captured image of the iris is often a cause for unclear images. Such optical artifacts may relate, for example to specular images and/or reflections (i.e. specularities) formed in the image plane and captured by the iris recognition identification system. When such specularities are present in the iris region of the captured image, this decreases the clarity of the iris image and as a result may increase the rate of false negative verification results.
One source of such undesired optical artifacts is reflective surfaces, such as the optical lenses of spectacles (i.e. eyeglasses, sunglasses or any other form of optical lenses worn on the nose and ears to cover the eyes). Capturing a clear image of an iris from a spectacle-wearing user is a problem for known iris recognition identification systems. One way in which this problem may be understood is to consider light illuminating a spectacle-wearing user's eye. A portion of the incident light is reflected by the spectacles, whilst the majority of the incident light is reflected by the eye (for present purposes we will ignore any absorption of the incident light occurring in either the spectacles or in the tissue of the human eye). Both portions of reflected light are subsequently captured and imaged by an image capture device, such as a camera. The captured image comprises an image of the eye, with an image of the spectacles and/or specular image superimposed on the iris region of the captured image of the eye. This superimposed image of the spectacles and/or specular image decreases the clarity of the iris portion of the captured image, and can have the undesired effect of increasing the rate of false negative verification results generated by iris recognition identification systems.
Currently known iris recognition identification systems require that the user remove their spectacles prior to image capture, to ensure that a clear image of iris may be captured. However, in many applications this solution is unsatisfactory, in particular in un-manned applications. Un-manned applications relate to applications of iris recognition identification systems where the process of iris image capture and iris verification is carried out in the absence of any operator. In manned applications an operator is present instructing the user how to position themselves, and to remove any spectacles such that a clear image of the iris may be captured. In contrast, in un-manned applications there is no operator present to assist the user.
It is an object of un-manned iris identification recognition systems to minimise the required active involvement of the user, and to simplify the image capture process. In this way, user-induced errors in the image capture process may be minimised.
It is an object of the present invention to provide a solution to the problem of undesired optical artifacts arising from a spectacle-wearing user, which solution minimises active user participation, to thereby improve the fidelity and usability of iris identification recognition systems in un-manned applications.